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Bangalore Fanfare Marks Final Breakthrough for Robbins EPB
On September 23, 2016, Bangalore’s last TBM for the city’s metro rail project broke through, marking the end of TBM tunneling on the Namma Metro phase 1. The Robbins-operated machine, known as “Krishna”, bored a 750 m (2,460 ft) drive through challenging conditions between Chickpet and Majestic stations. Cleanup and final commissioning of the tunnel will be completed in 2017, and is the last obstacle before owner Bangalore Metro Rail Corporation Ltd. (BMRCL) can open the Malleswaram-Majestic link. The TBM’s sister machine, “Kaveri”, completed a parallel tunnel in June 2016.
The success follows a gauntlet of challenges on the two tunnel sites. Due to severe delays on the original tunnel drives, Robbins was approached and asked to take over the operations of the remaining two competitor-manufactured TBMs in February 2015. After obtaining agreement from the project owner and the contractor, Robbins took over the responsibility for all aspects of the underground operations. “We provided a team of over 60 staff including TBM operators, TBM technicians, ring builders, a grouting team, and more. We were also responsible for running surface installations and equipment such as the grout batching plant, gantry cranes and power supply. Contractor Coastal Projects Ltd. (CPL) provided a team of people including surveyors, QC engineers, and loco operators who reported directly to our site management team,” explained Jim Clark, Projects Manager for Robbins India.
The Robbins crew carried out tunneling operations while the Chickpet station was being constructed around them to mitigate delays incurred before they took over project operations. The project’s most difficult challenges included a low overburden and unconsolidated ground along the alignment, and the discovery of several uncharted wells directly on the alignment. Difficult ground frequently prevented proper pressurization during cutting tool replacement, requiring a grout solution to be pumped in to fill voids and left to cure. Initially the curing process took up to 36 hours, but with improved application methods this was reduced to a 12-hour curing time.
Another challenge involved the sensitive building structures along the tunnel path. Issues with surface vibration, explained Clark, required that cutterhead speed be limited to 1.8 RPM during the day shift and 1.2 RPM during the night shift. Despite the obstacles, the TBMs advanced at rates of up to 50mm (2 in)/min in highly weathered rock.
“This is an industry first, wherein a TBM manufacturer has utilized their in-house expertise and knowledge to take on this level of responsibility for a project,” said Clark, addressing the magnitude of the successful breakthroughs. “The fact that it was “˜a first’ and we were successful in bringing this high-profile project back on track is a great achievement for The Robbins Company.”
Now that tunneling is complete, the North and South runs of the Namma metro will be connected–a line that, once in service, will carry an estimated 40,000 passengers daily. It is anticipated that Phase One of the metro will be opened in its entirety in 2017.
Hard-working Robbins TBM boring 28 km of tunnels below Indianapolis
On Tuesday, September 6, 2016, one of the longest-running Robbins TBMs embarked on its most extensive project yet. The 6.2 m (20.2 ft) Main Beam machine, owned by the Shea-Kiewit (S-K) JV, is boring the 8.5 km (5.3 mi) long White River Tunnel as the first in the next phase of the DigIndy wastewater tunnels below Indianapolis, Indiana, USA. In addition to that work, the machine will bore the Lower Pogues Run, Fall Creek, and Pleasant Run Tunnels™ scope of work totaling about 28 km (17 mi) through limestone and dolomite rock.
The rebuilt Robbins hard rock TBM was first used in Indianapolis on the 12.5 km (7.8 mi) long main tunnel, called the Deep Rock Tunnel Connector (DRTC). On that tunnel, the speedy machine achieved world records in its size class of 6 to 7 m (20 to 23 ft), including “Most Feet Mined in One Day” (124.9 m/409.8 ft); “Most Feet Mined in One Week” (515.1 m/1,690 ft); and “Most Feet Mined in One Month” (1,754 m/5,755 ft). “It’s nice to start the job with a machine that has already been proven and successful,” said Stuart Lipofsky, Project Manager for S-K JV.
However the DRTC was far from the TBM’s first job. The machine, originally built in 1980, has been used on New York City’s Second Avenue Subway, as well as projects in Massachusetts and Canada. Once the machine has completed the DigIndy network of tunnels, it will have bored more than 51 km (32 mi) of tunnel™n achievement making it one of the hardest working Robbins TBMs ever put into service. “The age of the machine wasn’t a concern for us, it was a positive. We knew it could perform in harder, abrasive rock,” said Lipofsky.
The machine was launched from the 67 m (220 ft) deep White River shaft following a refurbishment that included new motors, gearboxes, electronics, and other elements. As of the last week of September, the TBM has bored over 300 m (1,000 ft) of the White River Tunnel. About one mile into the White River Tunnel, the drive will bifurcate eastwards to bore the 2.7 km Lower Pogues Run Tunnel in front of Lucas Oil Stadium in downtown Indianapolis. The machine will then be backed up to the bifurcation point before continuing north for completion of the White River Tunnel.
As the machine bores, Robbins continuous conveyors remove muck in an extensive system that was highly successful at the DRTC. Much of the conveyor structure remains the same for the new tunnels, with new horizontal and conveyor belting provided. The conveyors will wind through curves as sharp as 300 m (1,000 ft) in radius, as the tunnels follow the path of the White River overhead.
The S-K JV has until 2021 to complete the White River and Lower Pogues Run tunnels for local owner Citizens Energy Group, and until 2024 to complete all the tunnels. The use of one TBM was seen as a positive: “The use of one machine was more efficient for our crews. The schedule allowed us to run with one TBM and we feel we can do it with one machine. It also was a less costly option than running two machines in terms of the owner funding the project,” said Dan Martz, vice president for J.F. Shea. Once complete, the EPA-mandated deep tunnel project will reduce the amount of raw sewage overflows and clean up tributaries along the White River.
The Robbins Company Announces Joe Lechner to SBU Sales
The Robbins Company announced the appointment of Joe Lechner to the role of Small Boring Unit (SBU) Sales Manager. With over 18 years of industry experience, the role is a natural career progression for Lechner. It brings him back to his early roots of working with SBUs, while more recently he worked with TBMs. Lechner can continue his success with the company in this new capacity with the trenchless division.
In his new position, Lechner will handle SBU sales and rentals for Robbins, assist customers in equipment specifications for projects, and provide full-spectrum customer support. In addition, Lechner will be responsible for many other tasks such as generating quotes for cutters and spare parts, shop scheduling, forecasting, internal operations for Robbins, and field service support, as needed.
“I want customers to know they can come to me with any issues. I have a good understanding of the industry and our business,” said Lechner. “I want to provide an all-around good experience. Robbins wants your project to be successful, with our equipment and support.”
Lechner began working with SBUs in 1998, starting in field service. When he wasn’t out in the field, he was building SBUs and cutters. He started up and commissioned SBU-As in the field, and transitioned over to working with TBMs worldwide in the mid 2000’s. With his diverse worldwide field experience, Lechner’s knowledge will continue to benefit Robbins and its customers.
Lechner said his goals as Sales Manager for the SBU product line for the next two years include increasing stocking levels and providing fast deliveries to customers. He noted the division is streamlining inspection quoting and repair processes to ultimately provide the most efficient services possible. With a few hundred machines in service, some of which are working around the clock, he anticipates product sales, rentals and repairs all will remain consistent moving forward.
“We’re lucky to have Joe working with Robbins,” said Tom Fuerst, Utility Tunneling Sales Manager. “With his background and extensive knowledge, he’ll easily implement the best solutions for our customers.”
Robbins Achieves another Breakthrough in Bangalore
In February 2015, Robbins, with its operating company Robbins India, was asked by Bangalore Metro Rail Corporation Limited to take over the operation and maintenance of two competitor-owned EPBMs. The machines were stalled due to low performance and financial issues from the Operating Contractor and lack of support by the original machine supplier. As the North-South Bangalore Phase 1 Metro tunnels were on the critical path, the BMRC looked to Robbins to step in and take over the troubled project. A Robbins/Robbins India team of 70 field service personnel refurbished and modified the existing equipment, both while in the tunnel and before relaunching the machines in Chickpet station. In addition, the on-site Robbins/Robbins India Team supervised all aspects of TBM excavation, segmental lining, mucking and grout plant operations since the relaunch of the machines for both drives.
“I am particularly proud of being involved in this project, and to support BMRC with the completion of this tunnel drive and bringing the project back on schedule. This is also the first time The Robbins Company has been responsible for the complete scope of operations on a project,” noted Jim Clark, Projects Manager with Robbins India. “One of the biggest challenges we faced was carrying out cutterhead interventions under compressed air in mixed ground conditions that consisted of varying grades of granite in the lower half of the face, and loose, unconsolidated material in the upper section of the face.”
Clark said that on numerous occasions, compressed air would percolate through to the surface, forcing crews to abort cutterhead interventions. They eventually found a solution by pumping a weak mix grout though the mixing chamber, and into the geology surrounding the tunnel face. The weak mix grout stabilized the ground sufficiently so the cutterhead interventions could be completed.
The Robbins crew carried out tunneling operations while the station was being constructed around them to mitigate delays incurred before they took over project operations. The project’s most difficult challenges included a low overburden and consolidated ground along the alignment, and the discovery of several uncharted wells directly on the alignment. In addition, the majority of the tunnel was bored directly beneath buildings constructed upon what is today considered substandard foundations.
This portion of the Phase One Metro tunnels runs from Chickpet to Majestic at Namma Metro. Once Krishna breaks through, the North and South runs of Bengaluru will be connected, allowing service to an average of 40,000 passengers daily. It is being completed under a tripartite agreement between Robbins India, Coastal Projects Limited, the lead contractor, and project owner, Bangalore Metro Rail Corporation Limited. It is anticipated Phase One will be open in its entirety by November, 2016.
Mexico's Crossover TBM makes its Mark for Robbins
On March 29, 2016, North America’s first Crossover TBM broke new ground in Mexico City. The 8.7 m (28.5 ft) diameter Robbins XRE™ –a cross between a rock TBM and an EPB–emerged into an intermediate shaft at Emisor Poniente (TEP) II.
The machine is undergoing some maintenance before continuing on to bore the final 3.2 km (2.0 mi) of tunnel. The customized TBM, for a consortium of Aldesem, Proacon, and Recsa, was chosen based on a number of parameters that included challenging ground conditions below an area to the west of downtown Mexico City.
The tunnel path travels through a mountain with cover as high as 170 m (560 ft), through fault zones and in a section with cover as low as 8.0 m (26.2 ft) above the tunnel crown. Much of the tunnel consists of andesite rock with bands of tuff, and softer material in fault zones as well as an 874 m (2,870 ft) long section in soft ground at the end of the tunnel.
“The geological profile of the project comprises six different lithologies, among them hard rock such as dacite. To get the best operation in both areas required use of dual mode technology such as the Crossover TBM,” said Enrique del Castillo of contractor Aldesem. The 8.7 m (28.5 ft) diameter Robbins XRE (Cross between Rock/EPB) is a design that allows for the TBM to effectively bore in both hard rock and mixed ground.
The machine setup includes a canopy drill and positioner for enhanced ground consolidation, as well as gear reducers to adjust torque and RPM based on ground conditions. The TBM, initially launched in hard rock mode, can be operated in EPB mode later on by switching out the belt conveyor with a screw and converting the cutterhead.
The Robbins Crossover machine began its journey in August 2015, and advance rates picked up quickly. Project records were set in January 2016 after the machine achieved a best day of 42.8 m (140 ft) and a best week of 185.1 m (607 ft). By mid-March the machine had bored through the first of the contact zones, a 30 m wide section of fractured and blocky rock. While the excavation through the contact zone was slow going, progress picked up again in the more competent rock. Final breakthrough is expected in autumn 2016.
Once complete, the 5.8 km (3.6 mi) tunnel will supplement an existing and overtaxed wastewater line built in the 1970s. The deep drainage tunnel will serve to prevent recurrent flooding in Valle Dorado, and will benefit the cities of Cuautital Izcalli, Tlalnepantla, and Atizapan de Zaragoza, an area with a total population of 2.1 million inhabitants.
Robbins EPB surmounts Chennai Metro Challenges
On January 27, 2016, a Robbins mixed ground EPB broke through at Chennai Metro, finishing up a challenging second drive that saw the full gamut of difficult conditions. The 1,027 m long second drive for the machine was part of Lot UAA-01 on Line 1 of the city’s metro, consisting of two parallel 1.0 km (0.6 mi) tunnels running from the Washermanpet area towards Chennai International Airport. Contractor Afcons Infrastructure Ltd. reflected on the breakthrough: “We are really proud of our executing team, who have maintained a high standard of quality. We didn’t record any water leakage or settlement at the surface, and we have demonstrated a high standard of safety in the tunnel during construction,” said Mr. Gopal Dey, Sr. Manager for Afcons.
The 6.65 m (21.8 ft) diameter Robbins EPB was designed to excavate granite, sand, silt, and clay with boulders up to 300 mm (12 inches) in diameter. The specialized design utilized a combination of 17-inch diameter disc cutters as well as soft ground tools. Small grippers located around the circumference of the machine’s shield allowed for cutterhead stabilization in harder ground, while additionally reacting the forces needed to pull the cutterhead back from the face in difficult conditions.
The TBM was launched on its initial drive in January 2012 from a 28 m (92 ft) deep starting pit. Challenges began nearly from the outset. The TBM bored into mixed face conditions that contained varying strengths of granite, from weathered to hard granite of 150 MPa (21,700 psi) UCS. The unexpectedly hard rock caused high cutter consumption rates and slowed advance.
A crew of Robbins Field Service personnel and engineers assisted Afcons in remedying the problem. Robbins India provided a geologist who carried out face mapping for the whole of the first drive, in both hyperbaric and open mode conditions on a daily basis. The data not only assisted the crew in operating the TBM, but also provided a comprehensive geological record for the second drive. With the data gleaned from the geological investigation, Robbins was able to advise Afcons on the optimal operating parameters to get through the difficult conditions, including cutterhead RPM, thrust pressure, penetration rate, and cutterhead torque. The parameters also resulted in a reduced cutter consumption rate.
Contractor Afcons was pleased with the help they received: “The Robbins Field Service team extended very good services to us, particularly in the mixed face & full face rock when they deployed their Geologist for face mapping. This helped us to understand the strata ahead of us, and based on this the TBM advance rate and operating parameters were decided,” said Mr. V. Manivannan, Executive Vice President for Afcons.
The TBM was launched on its second tunnel in February 2015. Conditions were just as difficult as the first drive, but now the team approached it with experience: “We experienced very high water pressure in this alignment, as the water table in Chennai is just 1.5 m (5 ft) underground and the strata above the crown included silty sand, clay and weathered rock. It was very important for us to maintain the earth pressure to reduce the inflow of water, and to avoid any settlement on the surface with proper grouting,” said Dey. Despite the challenges the TBM was able to complete a section below the Koovam River without any water flowing into the tunnel. The machine achieved up to 12.6 m (41 ft) in one day and 62 m (203 ft) in one week.
The TBM broke through into a receiving shaft, utilizing a unique setup for the second time that had the machine emerging under water. “These were the first breakthroughs in India under wet conditions in the retrieval shaft, which is 30 m (98 ft) below the ground level. The retrieval shaft was filled with Bentonite slurry 10 m (33 ft) from the base slab in order to arrest water entry from outside the diaphragm wall,” explained Manivannan.
The completed sections of tunnel will now be commissioned as part of Line 1, a 32.1 km (19.9 mi) long route in total with 14.3 km (8.9 mi) underground and a total of 17 stations. The southeastern Indian city of Chennai is a rapidly growing technological and industrial center with a population of more than 8.2 million people and a high need for alternate means of transportation.
Rosemont Double Shield on a roll for Robbins
In a large November 2015 ceremony attended by the mayor of Montreal, Quebec, Canada, and representatives from local media outlets, the Rosemont Reservoir tunnel construction came to a close. The challenging project gave good cause for celebration as crew members crowded around the cutterhead of the 3.0 m (9.8 ft) diameter Double Shield TBM that had emerged into an exit shaft.
Local contractor Foraction, Inc., headed the excavation of the 4.0 km (2.5 mi) long tunnel with a TBM launch in December 2014. Roger Lepinay, Equipment Manager for Foraction, Inc., praised the Robbins disc cutter wear in both limestone and harder rock formations: “I was impressed by the cutters, it was a nice surprise. They were quite long-lasting compared to other cutters I have used on jobs in the past.”
Lepinay characterized the ground as “almost ideal”, with a few difficult sections. “Below Montreal there is mostly thinly bedded limestone, with some shale and intrusive igneous rocks, mainly dykes and sills,” explained project geologist Brigitte Gagné for company Exp Service Inc. While the limestone averaged 100-150 MPa UCS, rock in the intrusives ranged from 100-300 MPa. The dykes and sills were as small as a few centimeters wide and as large as 8 to 10 m (26 to 33 ft) wide. The contractor was able to successfully navigate these sections despite the varying rock strengths. Even with geologic challenges including some water inflows and over-break in small sections, the contractor was able to achieve advance rates of up to 38 m (125 ft) per day in two shifts of 9.5 hours each. Much of the ground was self-supporting, though the contractor installed rock bolts every 2.5 m (8.2 ft) into portions of the tunnel crown, while mesh, rock bolts, and steel sheets were used in the sections of unstable rock.
The long tunnel drive at small diameter was carefully planned to optimize logistics. The contractor utilized a muck train that could accommodate two pushes worth of excavated material. The first kilometer (0.6 mi) was ventilated from the launch shaft, while three surface-driven 800 mm (32 in) diameter surveying wells at the 1, 2, and 3 km (0.6, 1.2, and 1.9 mi) marks ventilated the rest of the tunnel as the TBM progressed.
With the breakthrough, an important phase of the Rosemont Reservoir project is complete. The reservoir itself was built in 1960 to increase water supply to the city and a geotechnical study for the tunnel was carried out in 1977. However, other major infrastructure projects soon took priority and the project was placed on hold. By 2010, the population of the city had increased dramatically and problems with the existing reservoirs put the project back on the fast track. The large reservoir that sat idle for decades will now be used to improve much of the city’s water supply.
As of mid-January the contractor is working to ready the tunnel for installation of the carrier pipe, consisting of 2.13 m (84 in) I.D. pre-stressed concrete cylinder pipe (PCCP). Crews will then grout the pipe in place. There will be several more work stages to be carried out before the Rosemont Reservoir is finally reconnected to the water main network in 2019.
Rossaga Main Beam makes Historic Breakthrough
A crowd of crew members gathered to celebrate in front of a newly emerged hard rock TBM on December 10, 2015 in northern Norway, but their celebration was about more than just a breakthrough. The 7.2 m (23.6 ft) diameter Robbins Main Beam machine had traversed incredibly hard rock, water inflows, and more to become the first TBM in the country to break through in over 20 years.
The 7.4 km (4.6 mi) long headrace tunnel for the RøssÃ¥ga Hydroelectric Project offered up a number of challenges to the crew. “We bored through hard, quartz-rich rock with rock strengths up to 300 MPa (43,500 psi) UCS and softer karstic limestone with water ingress,” explained Tobias Andersson, TBM Manager for contractor Leonhard Nilsen & Sønner (LNS). Despite the geological challenges, the TBM performed very well and achieved a record production of 250 m (820 ft) advance in one week, as well as a high of 54 m (177 ft) in one day. Advance rates consistently ranged from 180 to 200 m (590 to 660 ft) per week throughout the project.
The hard and abrasive rock required both fine-tuning of the disc cutters and a learning curve with regards to TBM operation. “We overcame the rock by adapting driving parameters to the different geology, cutter wear and vibrations of the machine. We had regular maintenance, but most important of all we got really good at changing the cutters, with times down to 10 minutes per cutter change, which couldn’t have been done without good team work,” said Andersson.
It was the many cutter changes that prompted the close-knit team of LNS and Robbins to look for a better solution. “Extremely hard rock (above 250 MPa/36,300 psi) will always be a great challenge for any cutter. The very special features of the rock encountered combined with the extreme hardness made us go back to the Robbins Cutter Department to develop special cutter rings for the project. These rings increased the cutter life significantly for the project and contributed to the good production,” said Sindre Log, General Manager of Robbins Norway.
The Robbins TBM was launched following Onsite First Time Assembly (OFTA) in January 2014, less than twelve months after contract signing, and was from the outset designed for hard rock conditions. A Measurement While Drilling (MWD) system was included to analyze the ground conditions ahead of the TBM, while probe drilling was done systematically throughout the project. “This is a strong and simple machine ready to tackle hard rock conditions, but also designed to handle softer rock, which allowed for fast excavation. We had good support from competent Robbins field service,” said Andersson.
After all the obstacles, it was clear that the breakthrough ceremony celebrated a triumph of teamwork as well as a new chapter for TBMs in Norway. “Our whole jobsite was gathered for the event: LNS management, representatives from Robbins, and our client Statkraft. People said it was the best breakthrough event they had seen,” said Andersson. Now that tunneling is complete, project owner Statkraft will work to commission the tunnel and fill it with water by spring 2016.
Robbins Main Beam Ramps Up at the Mid-Halton Outfall Tunnel
The News in Brief:
- A 3.5 m (11.5 ft) Robbins Main Beam is a hard rock veteran, with a career spanning 32 years.
- With the 6.3 km (4.0 mi) Mid-Halton Outfall Tunnel under its belt, the Robbins Main Beam will have bored nearly 30 km (18.6 mi) of tunnels.
- The refurbished TBM was beefed up with modern VFDs, electronics, and a modified cutterhead for high-capacity tunneling in hard rock.
- Contractor STRABAG is in charge of tunnel construction in Ontario, Canada, as well as the construction of two deep shafts.
Full Story:
On July 22, 2015, a 3.5 m (11.5 ft) Robbins Main Beam TBM began a new chapter in its storied 32-year career. Originally built for the Terror Lake project in Alaska, the veteran machine has been used all over the world, most recently in Hong Kong. Including its new 6.3 km (4.0 mi) long tunnel for the Mid-Halton Outfall in Ontario, Canada, the machine will have bored nearly 30 km (18.6 mi) of tunnels since 1983.
The machine’s latest endeavor will not be without challenges. The rebuilt TBM has been beefed up for high-capacity tunneling in hard rock. Geology is expected to consist of laminated shale with interbedded limestone and siltstone layers and a maximum rock strength of 120 MPa UCS. “We have kept this a simple, streamlined Main Beam machine, but we modified the cutterhead with larger muck buckets, so material can be moved through it faster,” explained Robbins Project Manager Lynne Stanziale. In addition the TBM was outfitted with fully modernized VFDs, electronics, and high-capacity gearing and motors. The back-up system was also modified to make it more mobile through two 130 m (427 ft) radius curves that the TBM will have to navigate, one in each direction.
“The concept of using refurbished TBMs bears great opportunities for value-for-money constructors,” said Christian Zoller, Commercial Project Manager for contractor STRABAG. “Our TBM “˜Peggie’ is evidence of that–when well-maintained and professionally refurbished, the lifespan of these machines is extensive. We’re pleased to see that our client Halton Region has the forward-oriented mindset that allows STRABAG to provide its renowned high level of skill and quality, paired with the good value for money that a refurbished TBM yields.”
Contractor STRABAG, who has had several projects in Canada including the epic Niagara Tunnel project, is in charge of the works. In addition to the tunnel, STRABAG had to construct two deep shafts for the launch and exit of the TBM. The scheme involves two sections of tunnel designed to carry treated effluent water from a treatment plant in Oakville into Lake Ontario. The completed system will upgrade water treatment capacity in the Halton Region of Ontario.
The TBM was launched from a 12 m (39 ft) diameter, 62 m (203 ft) deep shaft and is ramping up production, having excavated over 300 m by early September 2015. “An ongoing challenge associated with the tunneling on this project is the requirement to drive the TBM downhill for the first 4 km (2.5 mi) of the tunnel. Keeping the water that infiltrates the tunnel from flowing directly to the cutterhead requires significant effort,” said Terry McNulty, Technical Project Manager for STRABAG.
Management of water inflows is not the only challenge. A portion of the drive will curve to run directly under Lake Ontario for 2.1 km (1.3 mi), though the tunnel is deep enough that it will remain in bedrock. Once the machine has completed its final bore under Lake Ontario, it will be backed out of the blind heading and removed from an 8.0 m (26 ft) diameter shaft in a local park.
“We can already see the potential performance that this TBM will have, once fully assembled and tested. We look forward to the continued support and cooperation with our partner Robbins on this endeavor,” said Zoller. Though the TBM has only recently started up, crews are moving forward with a plan to line the tunnel with mesh panels and ring beams if necessary. A cast-in-place liner will follow on after tunneling is completed in August 2017.
"Rock Girl" Revs Up
The News In Brief:
- A Robbins 3.96 m (13.0 ft) Main Beam TBM launched in spring 2015 to bore Hawaii’s longest tunnel.
- The 4.8 km (3.0 mi) Kaneohe-Kailua Wastewater Conveyance Tunnel is being built for the City and Council of Honolulu to stem overflows of wastewater after rain events.
- Southland/Mole JV is constructing the tunnel””the first of its scope to be built in the Hawaiian Islands.
- As of June 2015, the Robbins TBM had excavated more than 300 m (1,000 ft), and was boring at a rate of 12 to 15 m (40 to 50 ft) per day in basalt rock.
In the spring of 2015 by the idyllic shores of Oahu, a Robbins 3.96 m (13.0 ft) diameter Main Beam TBM began its long journey. The TBM started its excavation on a 4.6 km (2.8 mi) drive for a new sewer tunnel in Kaneohe, Honolulu, Hawaii, USA. The machine, nicknamed Pohakulani, meaning “Rock Girl” in Hawaiian, launched from a 23 m (74 ft) deep starter tunnel on a mission to bore through almost 4.8 km (3.0 mi) of basalt bedrock. Contractor Southland/Mole JV is building the Kaneohe-Kailua Wastewater Conveyance Tunnel for the City and Council of Honolulu, which will improve wastewater infrastructure by eliminating overflows during rain events.
The deep tunnel option was not the first design considered for the project: preliminary plans called for a smaller tunnel traveling under the bay. As Kaneohe Bay is an environmentally-sensitive area, a deep tunnel remained an attractive option. Richard Harada, of project consultant Wilson Okamoto Corporation, explains the ultimate decision: “A number of factors were considered in making the decision to build a deep tunnel including reliability, construction costs, life cycle costs, environmental impacts, constructability and qualified contractor availability.”
During the tunnel design phase, it was decided that the tunnel route should travel inland and deeper underground in order to bypass one of the few residential areas along the alignment. Designers introduced an isolated curve in the tunnel alignment of 150 m (500 ft) radius, requiring the TBM to be designed with a unique back-up system. There will also be operational procedures when crews navigate the tunnel curve, requiring the machine to be operated using half strokes rather than a full TBM stroke.
The curve is not the only unusual aspect of the tunnel; in fact, a tunnel on this scale has not been built in the Hawaiian Islands before. Everything from the logistics of the tunnel operation to pre-grouting sections ahead of the TBM for groundwater control are new to the Aloha State. Director of Southland, Tim Winn, elaborates: “There has not been a Tunnel Boring Machine of this size in the Hawaiian Islands or a tunnel of this length. The tunnel is being driven from an active Water Treatment Plant (WTP), and space is at a premium. There are also simultaneous contracts being performed there outside the scope of our work.” He adds that although there have been challenges, teamwork has been key: “Robbins Field Service has been extremely valuable during assembly and commissioning of the TBM.” As of June 2015, the TBM has excavated more than 300 m (1,000 ft), and is boring at a rate of 12 to 15 m (40 to 50 ft) per day in basalt rock. Rock bolts, steel arches, wire mesh, and ring beams are being installed as necessary.
Upon completion, the deep tunnel will enhance water treatment capabilities and further aid in ceasing non-compliant, uncontrolled or moderately treated wastewater discharges. The Main Beam TBM is estimated to end its journey in eight to ten months at the Kaneohe Wastewater Pre-Treatment Facility.